Energy transformation is the process of transforming one form of energy to another. The sun, wind, water, natural gas, coal, oil, are examples of energy sources. Sound, like the sound made by someone's vocal cords, also carries energy.
A transducer is a device which converts one form of energy into another. In an acoustical context, this usually means converting sound energy into electrical energy. Sound is a wave which is created by vibrating objects and propagated through a medium from one location to another. A wave can be described as a disturbance that travels through a medium, transporting energy from one location to another location. The medium is simply the material through which the disturbance is moving.
Usually the medium for a sound wave is air, though it could be any material such as water or steel. Particles in the medium are periodically displaced by a sound wave, and thus oscillate. The energy carried by the sound wave converts back and forth between the potential energy of the extra compression of the medium and the kinetic energy of the oscillations of the medium.
The medium is simply a series of interconnected and interacting particles. The vibrating object which creates the disturbance could be the vocal chords of a person, the vibrating string of a guitar, or the vibrating diaphragm of a radio speaker. The sound wave is transported from one location to another by means of particle-to-particle interaction. If the sound wave is moving through air, then as one air particle is displaced from its equilibrium position, it exerts a push or pull on neighboring air particles. This particle interaction continues throughout the entire medium, with each particle interacting and causing a disturbance of its nearest neighbors.
The energy in sound waves can be transformed into electrical energy. Microphonics is the generation of electrical signals when an object or component is excited by audio sound waves. For example, when an electronic device or appliance (such as a telephone, computing device, etc.) having a communication wire or conduit leading away from it is excited by audible noises, the audible noises affecting the device result in a corresponding electrical signal transmission along the wire or conduit. While such unintended transmissions may be typically disregarded as a negligible occurrence with little consequence, the unintended signal voltages and transmissions resulting from audible signals become problematic when these voltages can be monitored or intercepted outside a secure location through an Ethernet wire or other conductor. For example, the intelligible speech that can occur in the audio band between 20 Hz and 20 kHz in a secure room or location can be transduced by an electronic device and excite communication lines leading away from the site, which could result in the unintended and/or undesirable transmission or disclosure of sensitive information.
The Telecommunications Security Group (“TSG”) standard No. 5 specifies the minimum required performance for a telephone that can be located in a sensitive discussion area. The TSG standards contain guidance involving telephone systems located in areas where sensitive government information is discussed, processed, and stored. The National Telecommunications Security Working Group (“NTSWG”), formerly known as the Telecommunications Security Group (“TSG”), is a Joint Working Group of the Committee on National Security Systems which was established to protect National Security Systems. The NTSWG is responsible for security countermeasures for all telecommunications systems and components used within a classified information processing area. The NTSWG is the primary technical and policy resource in the US Intelligence Community for all aspects of the technical surveillance countermeasures program involving telephone systems. The acceptance criteria and tests presented in the TSG Standard No. 5 are for use in manufacturing and procurement of telephone instruments.
For example, in order to comply with the TSG Standard No. 5, while a telephone is on-hook, i.e. in the idle state, the telephone must not be able to pick up and transmit audio to the mounting cord. The term “on-hook” refers to hanging up or otherwise deactivating communication of the telephone/communication device. The telephone must not exhibit intrinsic microphonic behavior with respect to any of the conductors leaving the body of the instrument that further leave the secure area where the telephone is located, e.g., the specific office or room. The non-microphonic characteristic must be sustained independent of all environmental stimuli, including acoustic and electromagnetic fields, voltages, or commands that could be impressed on mounting cord or power supply wires.
Also, without a manual action by the user, neither the system nor an incoming call is permitted to alter the telephone's non-microphonic characteristics or cause it to be off-hook. As used herein, the term “off-hook” refers to lifting the handset from the cradle or otherwise activating telephone/communication device for communication. The ideal condition for on-hook audio security is that the telephone cannot by any means be caused to produce audio when it is on-hook. For real telephones, however, there is always a possibility that accidental or deliberate modifications could cause it to pass audio. Measures to minimize this possibility must be applied. The design and construction of a telephone or other communication device must not facilitate any modification that could cause it to pass audio or become microphonic while on-hook.
Of note, although the present invention is discussed and referenced with respect to compliance with TSG Standard No. 5, such reference is intended to include other telephone microphonic standards such as the Committee on National Security Systems (“CNSS”) Instructions such as CNSS Instruction No. 5001.
Accordingly, it is desirable to provide a method and system to filter and/or remove microphonic signals that could be unintentionally transmitted from communication devices coupled to a network. It is further desirable to provide a method and system to filter microphonic signals that is readily integrated with numerous existing devices and systems already in place.